The present invention relates to a fence sensor, and more particularly to a crime prevention sensor for a fence which can detect the presence of an object that approaches or makes contact with the fence.
Among the conventional crime prevention sensors for a fence for detecting an intruder, there has been known an electric field formation type sensor as disclosed in Japanese Patent Laid-Open Publication No. 9-237389. This is a type in which an electric field is generated by supplying sinusoidal current to electric wires embedded in the fence, and an alarm device is actuated when a change of the electrostatic capacity is detected that occurs due to an intrude approaching the fence.
In addition, there has also been known a crime prevention sensor in which an emitting part of infrared rays and a receiving part for receiving the emitted infrared rays are installed in the vicinity of the fence in order to establish an infrared ray detection region along the fence. In this sensor, when an interception of infrared rays by an intruder is detected, an alarm device is actuated.
The electric field formation type sensor uses a sinusoidal wave to generate an electric field, so it has a problem that it becomes a source of noise in telephone lines or electronic circuits found in the vicinity of the fence. Accordingly, installation sites for the sensor are limited.
Moreover, the electric field formation type sensor has a detection region defined by the region where electric wires are laid within the fence, so that it has a problem that it gives restrictions on the fence design.
Besides, the electric field formation type sensor has another problem that the power consumption increases due to the necessity that the electric field has to be maintained all the time.
Furthermore, with respect to the infrared sensor, the detection region between the light emitting part and the light receiving part needs to be formed in a linear shape, so that it has a problem that a detection region cannot be formed along a fence having a curved surface structure.
It is an object of the present invention to provide a fence sensor with an excellent detection stability that resolves the problems associated with the electric field formation type sensor and the infrared sensor described above without requiring electric current for generating an electric field or infrared rays.
A fence sensor defined by claim 1 comprises:
a detection electrode;
a reference electrode insulated from the detection electrode;
a chargeable member insulated from both of the detection electrode and the reference electrode, the chargeable member being arranged such that at least a part of the chargeable member is situated within a detection region of the detection electrode, and the chargeable member being formed from a conductor; and
a detection circuit for detecting a change in the electrostatic capacitance between the detection electrode and the reference electrode that is generated by the presence of an object to be detected within the detection region.
In this structure, when the electrical charges on the chargeable member are increased by the presence of the object within the detection region of the chargeable member, the electrostatic capacitance between the detection electrode and the reference electrode is changed. According to the present invention described above, the fence sensor can detect the presence of the object within the detection region by detecting such a change in the electrostatic capacitance between the detection electrode and the reference electrode. Accordingly, the fence sensor of this invention does not require the formation of an electric field or the use of infrared rays.
For example, if an intruder approaches the detection region, electrostatic induction is generated in the conductive chargeable member due to the charge on the body of the intruder, thus increasing the amount of the charge on the chargeable member. Since the chargeable member is insulated from both of the detection electrode and the reference electrode, the charges on the chargeable member will not move directly to these electrodes as currents. However, since the chargeable member is found within the detection region of the detection electrode, the increase in the charges on the chargeable member forms an electric field in the detection region of the detection electrode, and causes an increase in the charge on the detection electrode. Consequently, the electrostatic capacitance between the detection electrode and the reference electrode is increased. When the increase in the electrostatic capacitance exceeds a detection threshold of the detection circuit, the detection circuit outputs a detection signal.
Further, the use of the chargeable member makes it possible to form a detection region with wider area. For example, when a wide area of the sidewall of the fence is formed as a detection region, the increase in the detection region can simply be achieved by the installation of a chargeable member on the entire sidewall of the fence. However, if the detection electrode and the reference electrode are installed over a wide area, the electrostatic capacitance between the detection electrode and the reference electrode becomes extremely large in the case of absence (static state) of an object in the detection region of the detection electrode.
When the electrostatic capacitance between the detection electrode and the reference electrode is extremely large as in the above, the increased amount of the charge on the detection electrode in the charged state (that is, in a state that an object is found within the detection region) will be relatively extremely small compared with the amount of the charge in the static state. Because of this, the detection circuit has to detect an extremely large increase, relatively speaking, in the amount of the charge, thus impairing detection stability or causing inability of detection. For these reasons, the fence sensor of this invention utilizes the chargeable member. According to such a fence sensor, it is possible to stably detect an object within a wide detection region. Further, it is also possible to achieve the detection without being accompanied by an increase in the electrostatic capacitance between the detection electrode and the reference electrode in the static state.
Here, there is no limitation on a fence in which the fence sensor of this invention is to be installed. Examples of such a fence includes a wall formed of concrete or stone; a palisade formed from support pillars arranged with a prescribed distance apart and a metallic net spread between the support pillars; and the like. Further, such a fence may be installed indoors, and may also be installed outdoors. In addition, the fence sensor of this invention may be installed in a fence so that the detection region covers the entirety of the fence. Further, the fence sensor may also be installed so that the detection region covers a part of the fence (e.g., handrails of the fence).
Further, the use of the fence sensor is not limited to the purpose of crime prevention. For example, a fence sensor of this invention may be installed on a fence in the rear of a parking lot in order to give a warning about the approach of a vehicle to the fence. According to such a fence sensor, it is possible to prevent collision of a vehicle with the fence.
The fence sensor defined by claim 2 further comprises water film separation means for separating a water film on the surface of the chargeable member from a water film grounded to the earth.
A fence sensor defined by claim 3 comprises:
a detection electrode;
a reference electrode insulated from the detection electrode;
a chargeable member arranged such that at least a part of the chargeable member is situated within a detection region of the detection electrode, the chargeable member being formed from an insulator; and
a detection circuit for detecting a change in the electrostatic capacitance between the detection electrode and the reference electrode that is generated by the presence of an object to be detected within the detection region.
When an intruder approaches the chargeable member (which is an insulator), induced polarization is generated in the chargeable member due to the charges on the body of the intruder. Then, an electric field is generated in the detection region of the detection electrode by polarized charges generated by the induced polarization. As a result of the formation of the electric field, the electrostatic capacitance between the detection electrode and the reference electrode is increased, and the detection circuit detects the presence of the intruder.
Here, there is no limitation on material used for making the insulator, and shape of the insulator. For example, the insulator may be prepared using material such as wood, a synthetic resin, stone, earthenware, concrete, and the like.
In the fence sensor defined by claim 4, the detection electrode and the reference electrode are partially or completely concealed by the chargeable member.
Since the fence sensor of this invention has the detection electrode and the reference electrode which are concealed by the chargeable member, it tends to be difficult to make approach to or direct contact with both the electrodes. Because of this, according to the present invention, it is possible to prevent breakdown of the detection circuit by electrostatic sparks. This arrangement is made for avoiding the following undesirable case. That is, when the air is dry, the charge quantity on the body of the intruder is extremely large. In such a condition, if both the detection electrode and the reference electrode are exposed, electrostatic sparks are generated between the electrodes and the human body, and its high voltage current will instantly destroy the detection circuit that is connected to these electrodes.
Further, according to the fence sensor of this invention, the chargeable member is insulated from both the detection electrode and the reference electrode. Consequently, it is possible to make the chargeable member absorb the high voltage current by the electrostatic sparks, thus making it possible to prevent a high voltage current from directly flowing to the detection circuit. In addition, the fence sensor of this invention has an advantage that an easy revealing of the presence of the sensor can be avoided because of the concealment of the electrodes by the chargeable member.
In this invention, the detection electrode and the reference electrode are partially concealed. This means to conceal only a portion that has a high possibility of making approach to or contact with the human body, that is, to conceal only a portion where electrostatic sparks tend to be generated between the electrodes and the human body. In addition, it means to conceal only portions that make these electrodes readily identifiable from the outside.
In the fence sensor defined by claim 5, the reference electrode is connected electrically to the ground or a building.
When the reference electrode is connected to the ground, it is possible to set the detection threshold higher, since the electrostatic capacitance between the detection electrode and the reference electrode in the charged state can be increased compared with the case where it is not connected to the ground. Therefore, the ratio of the signal to noise generated by the environment (i.e., S/N ratio) can be enhanced, and the detection stability can be improved.
Here, the connection with the ground means to connect the reference electrode to the ground in the case where the fence is installed on the ground. Further, the connection with the building also means to connect the reference electrode to the building in the case where the fence is installed in the terrace or the like of the building. In this connection, the electrical connection will not involve the use of a grounding resistance as a necessary condition.
In the fence sensor defined by claim 6, the chargeable member is provided with water repellent means.
For example, in the case where the chargeable member is made of concrete which is an insulator, if moisture infiltrates into the chargeable member, the migration of charges within the chargeable member is facilitated by the hydrogen ions that are charged positively, and thus the chargeable member is converted to a state that resembles to that of a conductor.
Accordingly, the rate of increase of the electrostatic capacitance of the detection electrode in the static state and the electrostatic capacitance in the charged state decrease relatively. Because of this, the detection circuit has to detect the increase rate that is relatively decreased, and it becomes necessary to enhance the detection precision.
For this reason, in this invention the water repellent means is provided in the chargeable member in order to prevent infiltration of moisture into the interior of the chargeable member. This makes it possible to keep the charge quantity on the chargeable member in the static state, and thus a high detection precision is maintained.
The fence sensor defined by claim 7 further comprises directivity control means for limiting the direction of the electric lines of force of the detection electrode.
According to the fence sensor having such directivity control means, for example, it is possible for the fence sensor to detect an intruder who tries to jump over the fence, and also possible to avoid detecting a pedestrian who passes along the fence.
In the fence sensor defined by claim 8, the directivity control means is a shielded electrode connected to the reference electrode. This fence sensor has the shielded electrode connected to the reference electrode, so that it is possible to completely shield off unwanted electric lines of force of the detection electrode.
The fence sensor defined by claim 9 further comprises at least one inter-electrode chargeable member which is disposed between the detection electrode and the reference electrode, and which is insulated from both of the detection electrode and the reference electrode. This fence sensor is capable of stabilizing the sensitivity of the detection electrode, and reduce the detection threshold of the detection circuit by equipping it with the inter-electrode chargeable members. Accordingly, the detectable region of the sensor can be extended.
In the fence sensor defined by claim 10, the detection electrode includes first and second detection electrodes which are insulated from each other, and the detection circuit includes comparison means for comparing electrostatic capacitance between the first detection electrode and the reference electrode with electrostatic capacitance between the second detection electrode and the reference electrode.
In the fence sensor defined by claim 11, the detection electrode and the reference electrode are constructed from a plurality of sets of detection electrode and reference electrode, in which the plurality of the detection electrodes are electrically connected to each other, the plurality of the reference electrodes are electrically connected to each other, and the plurality of detection electrodes and the plurality of the reference electrodes are connected to the detection circuit. This fence sensor can realize a wide range of detectable region at a low cost by detecting the changes in the electrostatic capacitances between the plurality of detection electrode and reference electrode sets using a single detection circuit.
A fence sensor defined by claim 12 comprises:
a detection electrode;
a reference electrode insulated from the detection electrode;
a detection circuit for detecting a change in electrostatic capacitance between the detection electrode and the reference electrode that is generated by the presence of an object to be detected within the detection region; and
a capacitor connected in series between the detection circuit and the detection electrode, the capacitor being disposed separated from the detection electrode.
The fence sensor defined by claim 13 further comprises electrostatic spark preventing means which is disposed between the detection circuit and the detection electrode.
A fence sensor defined by claim 14 comprises:
a detection electrode;
a reference electrode insulated from the detection electrode;
a detection circuit for detecting a change in electrostatic capacitance between the detection electrode and the reference electrode that is generated by the presence of an object to be detected within the detection region; and
water film separation means for separating a water film on the surface of the detection electrode from a water film grounded to the earth.
In the fence sensor defined by claim 15, the water film separation means has a trench with a width of 6 mm or more, in which the trench is opened downward.
In the fence sensor defined by claim 16, the water film separation means has a main trench with a width of 6 mm or more and an auxiliary trench with a width of less than 6 mm, in which the main trench is opened downward, and the auxiliary trench is opened downward and provided in the main trench.
A fence sensor defined by claim 17 comprises:
a detection electrode;
a reference electrode insulated from the detection electrode; and
a chargeable member insulated from both of the detection electrode and the reference electrode, the chargeable member being formed from a conductor or an insulator, and the chargeable member being arranged such that at least a part of the chargeable member is situated within a detection region of the detection electrode.
A sensor for an ascending and descending member defined by claim 18 comprises:
a detection electrode;
a reference electrode insulated from the detection electrode;
an ascending and descending member insulated from both of the detection electrode and the reference electrode, the ascending and descending member being formed from a conductor or an insulator, and the ascending and descending member being arranged such that at least a part of the ascending and descending member is situated within a detection region of the detection electrode; and
a detection circuit for detecting a change in electrostatic capacitance between the detection electrode and the reference electrode that is generated by the presence of an object to be detected within the detection region.
The sensor for an ascending and descending member according to the present invention belongs the same technical field and has the same problems to be solved as those of the fence sensor described above. Therefore, this fence sensor is also capable of detecting an intruder or the like who steps on the ascending and descending member that is a chargeable member. In this sensor, a change in the electrostatic capacitance between the detection electrode and the reference electrode, generated by the presence of an object to be detected within a detection region, is detected by the detection circuit.
Examples of the ascending and descending member include a ladder and an emergency stairway, and this ascending and descending member mainly designates a member on which a human being steps when ascending and descending. For example, in the case of a ladder, a rung of the ladder is made of a stainless steel pipe, and two electric wires forming a detection electrode and a reference electrode are strung inside the rung. In the case of an emergency stairway, a step is made of concrete, and an electrode member having two conductive layers forming a detection electrode and a reference electrode is attached to the rear surface of the step.
A sensor for an ascending and descending member defined by claim 19 comprises:
a detection electrode;
a reference electrode insulated from the detection electrode; and
a chargeable member insulated from both of the detection electrode and the reference electrode, the chargeable member being formed from a conductor or an insulator, and the chargeable member being arranged such that at least a part of the chargeable member is situated within a detection region of the detection electrode.